[XFS] Don't update mtime on rename source

As reported by Michael-John Turner XFS updates the mtime on the source
inode of a rename call in case it's a directory and changes the parent.

This doesn't make any sense, is not mentioned in the standards and not
performed by any other Linux filesystems so remove it.

SGI-PV: 983684

SGI-Modid: xfs-linux-melb:xfs-kern:31364a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Barry Naujok <bnaujok@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>